THE RELATIONSHIP OF NITROGEN AND DEFOLIATION ON ESTABLISHMENT OF BAREROOTED DECIDUOUS PLANTS

Authors: GUIHONG, BI - OSU; Scagel, Carolyn; FUCHIGAMI, LESLIE - OSU

Submitted to: Ornamentals Northwest Show
Publication Type: Abstract Only
Publication Acceptance Date: 8/17/2003
Publication Date: 8/20/2003
Citation: THE RELATIONSHIP OF NITROGEN AND DEFOLIATION ON ESTABLISHMENT OF BAREROOTED DECIDUOUS PLANTS. Guihong, B.I., Scagel, C.F., Fuchigami, L.

Interpretive Summary: Natural defoliation of most deciduous plant in the NW often occurs late in the fall. Deciduous nursery plant growers would like to harvest plants before the rainy season. To decrease grower harvest costs and improve the performance of bareroot nursery stock during establishment, growers need to promote early defoliation as well as maximize mobilization of nutrients from leaves to stems and roots. During normal leaf senescence, approximately 50% of the nitrogen (N) in leaves is mobilized back to the plant. Among the N used for new growth in the spring, 90% comes from N in these reserves. Use of defoliants decreases these N reserves. After defoliant treatment, the leaves that fall off are green and more than 25% of the total tree N can be lost. This can result in less N for new growth in the spring and plant may suffer dieback, delayed bud break, and poor growth. To correct for these problems associated with using defoliants, a grower must maximize the mobilization of leaf N to storage stem and root tissues. This can be done by using a foliar application of N fertilizers. Plants can absorb urea from leaves. Uptake of urea from foliar application in the fall has been found to occur primarily in the first two days after application. 30-60% of the absorbed N is translocated out of the leaves to storage in stems and roots within 20 days after urea application. Application of foliar urea in the fall prior to or with chemical defoliants can potentially be used to increase N reserves in plants as well as attain the benefits of early defoliation. This increase in N reserves could then result in improved establishment and growth of plants the following spring.

Technical Abstract: Natural defoliation of most deciduous plant in the NW often occurs late in the fall. Deciduous nursery plant growers would like to harvest plants before the rainy season. To decrease grower harvest costs and improve the performance of bareroot nursery stock during establishment, growers need to promote early defoliation as well as maximize mobilization of nutrients from leaves to stems and roots. During normal leaf senescence, leaf proteins break down to amino acids and are mobilized back to the plant. The rapid decrease in leaf N begins 3 to 4 weeks prior to abscission and up to 50% of total leaf N can be mobilized back during senescence. Among the N used for new growth in the spring, 90% comes from N in these reserves. After treatment with defoliants, the leaves fall off before any significant N mobilization can occur and trees can lose more than 25% of the total tree N. This results in less N used for new growth in the spring and plants may suffer dieback, delayed bud break, and poor growth. To correct for the problems associated with using defoliants, a grower must maximize the mobilization of leaf N to storage stem and root tissues. This can be done by using foliar application of N fertilizers such as urea. Uptake of urea from foliar application in the fall occurs primarily in the first two days after application. 30-60% of the absorbed N is translocated out of the leaves to storage in stems and roots within 20 days after urea application. Application of foliar urea in the fall prior to or with chemical defoliants, can potentially be used to increase N reserves in plants as well as attain the benefits of early defoliation. This increase in N reserves could then result in improved establishment and growth of plants the following spring.